This invention relates to cationic, water soluble, high molecular weight acrylamide derived polymers and processes for making them. The polymers are useful for treatment of waste water to separate efficiently the waste from the water.
There is a high and increasing demand for high molecular weight, cationic polyelectrolytes for water treatment, especially for treatment of waste water. There are available certain such high molecular weight polyelectrolytes. For example, high molecular weight polyacrylamide has been modified by grafting processes to provide cationic polyelectrolyte polymers which are said to be useful for water treatment. For example, in U.S. Pat. No. 3,707,465, there is disclosed grafted polyacrylamide polymers in which high molecular weight polyacrylamide is said to be grafted by oxyamination using base catalysis. Relatively low level of grafting was obtained according to the patent (not more than 20 percent grafting). It is indicated in the prior art that the effectiveness of the oxyaminated polyacrylamides in the flocculation water purification process is dependent upon the pH of the waste water (preferably a pH between 6 and 4.3) and the presence of a water soluble inorganic coagulant such as alum. It has been noted that the structure of the oxyaminated polyacrylamide polymers of that prior art was not disclosed.
Prior art related to the formation of cationic polymers suggest either treatment of aqueous polymer solutions with glycidyltrimethylammonium chloride (Reinwald, U.S. Pat. No. 3,707,465) or copolymerization using comonomers such as 2-hydroxy-3-acryloyloxypropyltrimethylammonium chloride (Sobolev, U.S. Pat. No. 3,329,706). In order to have good flocculating properties, polymers must have high molecular weights and high concentrations of cationic groups. Aqueous solutions of high molecular weight polymers, however, have extremely high viscosities and are difficult to handle; they may have, therefore, generally polymer concentrations of less than 2%. Treatment of such diluted solutions with glycidyltrialkylammonium chloride results primarily in hydrolysis of the glycidyl moiety; any reaction (or grafting) with the polymer, if it occurs at all, results only in insignificant incorporation of cationic groups. These reaction products, therefore, do not exhibit adequate flocculant characteristics. Copolymerization of monomers such as acrylamide with monomers such as 2-hydroxy-3-acryloyloxypropyltrimethylammonium chloride on the other hand, results in products that may have higher concentrations of cationic groups but have very low molecular weights. Thus, it is quite apparent that conventional practices can hardly be expected to yield efficient flocculants containing cationic groups derived from glycidyltrialkylammonium salts.
It is therefore an object of this invention to provide a novel class of cationic, water-soluble, high molecular weight polymers which are efficient flocculants.
It is a further object to provide polyelectrolyte polymers which are effective over a broad range of pH in the water to be treated and are substantially free of unwanted units.
It is another object of this invention to provide processes which enable a high degree of grafting to produce good yields of the desired cationic, high molecular weight polymers of the invention.